1. Field of the Invention
The present invention relates to an actuator configured to move a moving portion with expansion/contraction of a shape memory alloy and to an image pickup apparatus used in a medical apparatus such as an endoscope and capable of changing optical performance by the actuator.
2. Description of Related Art
In recent years, endoscopes are widely used in the medical and industrial fields. Endoscopes have an elongated insertion portion inserted in a tube to enable observation in the tube.
An image pickup apparatus including an objective optical system formed of a plurality of objective lens groups for observing the interior of a tube, and a solid-image pickup device or the like such as a CCD is generally provided in a distal end portion at a distal end side in the insertion direction in an insertion portion of an endoscope, e.g., an electronic endoscope, which is configured to pick up an image of an observed portion in a tube formed by the objective optical system.
A zoom endoscope is well known in which at least one lens in a plurality of objective lens groups in an objective optical system is provided as a moving lens capable of moving in an optical axis direction of the objective optical system, and in which optical characteristics including the depth of focus of the objective optical system on an observed portion, the observation magnification and the angle of view can be changed by moving the moving lens in the optical axis direction. By observation using the zoom endoscope in a case where the zoom endoscope is, for example, an endoscope for medical use, mucous membranes, the structure of capillaries, etc., at an observed position in a body cavity can be observed.
Various mechanisms have been proposed as a mechanism for moving in an optical axis direction a moving lens provided as a moving member as described above. For example, Japanese Patent Application Laid-Open Publication No. 2004-129950 discloses a technique to move a moving lens in an optical axis direction by extending and contracting in the optical axis direction a shape memory alloy (hereinafter referred to as SMA) wire extending in the optical axis direction and having its one end fixed to a projection formed integrally on a moving lens frame in which the moving lens is provided. To extend or contract the SMA wire, the SMA wire is set in an energized state or in a non-energized state. That is, the publication discloses a technique to move a moving lens in an optical axis direction by using an actuator having an SMA wire.
Japanese Patent Application Laid-Open Publication No. 2005-003867 discloses a technique to move a moving lens in an optical axis direction by using repellency between a north pole of a drive magnet and a north pole of a follower magnet or repellency between a south pole of the drive magnet and a south pole of the follower magnet. The follower magnet is provided along an optical axis direction on a moving magnet holder fixed on a moving lens barrel holding a moving lens. The drive magnet is held on a drive magnet holder movable in a clockwise direction and in a counterclockwise direction. The drive magnet holder is provided on the outer peripheral side of the moving lens in a diametric direction of the moving lens than the driven magnet. That is, the publication discloses a technique to move a moving lens in an optical axis direction by using an actuator having a follower magnet and a drive magnet.
Other techniques to move a lens moving member in an optical axis direction by magnetic action have been disclosed. For example, Japanese Patent Application Laid-Open Publication No. 2005-227705 discloses one for a lens drive apparatus. Further, Japanese Patent Application Laid-Open Publication No. 2006-276798 discloses a technique to open and close a shutter and a diaphragm by magnetic action in an image pickup apparatus.
Among configurations including a lens movable by changing the optical focal position, the lens drive apparatus described in Japanese Patent Application Laid-Open Publication No. 2005-227705 or the image pickup apparatus described in Japanese Patent Application Laid-Open Publication No. 2006-276798 is provided with a variable diaphragm for adjusting the optimum brightness, i.e., the amount of light in the optical system.